20,25-Diazacholesterol, an inhibitor of cholesterol biosynthesis, produces a myotonic syndrome in rats. Abnormal electrical and contractile activity appears in parallel with increasing desmosterol levels in surface membranes. This alteration in sterol composition correlates with a major change in apparent microviscosity of the membrane hydrocarbon core and significant activation of the membrane Na+K+ATPase. We will study the specific relationship between desmosterol/cholesterol membreane ratio and the physical properties of membrane lipids using steady-state and time-resolved fluorescence techniques in muscle membranes and artificial liposomes. We will study the relationship between desmosterol content, membrane physical properties and intrinsic membrane protein activity by studying rotational relaxation rates of intrinsic membrane proteins and extending our kinetic studies of Na+K+ATPase to purified enzyme in reconstituted liposomes of controlled lipid composition. We will extend our understanding of excitation and E-C coupling in these abnormal membranes with voltage clamp and skinned fiber techniques, again seeking to relate abnormality of function to parallel studies of membrane chemical.